At present, there are wireless communication systems which demand the use of antenna diversity, such as in fourth generation Long Term Evolution (4G LTE) communication systems. These LTE systems can utilize different antenna configurations including multiple-input, multiple-output (MIMO) spatial-diversity antennas, multiple-input, single-output (MISO) transmit-diversity antenna, and single-input, multiple-output (SIMO) receive-diversity antennas, including beamforming variations. As a result, there is a need to properly tune these antennas. This can be problematic if a given antenna is a receive-only antenna, which is the case for some LTE systems, for example.
In order to tune an antenna, the antenna must first be measured and then that information can be used to determine the degree of tuning that is applied to the antenna. This measurement is normally achieved by measuring the ratio of energy applied to the antenna versus the energy measured reflecting from the antenna. In the case of most antennas, the antenna measurements can be done during manufacturing, and the results used to compensate the antenna while in use.
However, this approach can be problematic when dynamic variables affecting the antenna(s) while in use need to be compensated for. As an example; if the device that contains the antennas is of the handheld type, the presence of a user's hand holding the device may detune the antennas. Therefore, the antenna measurements made at the factory during manufacturing of the device may no longer be valid in the presence of hand-loading of the antenna(s).
One solution is to perform active antenna measurements while the device is in use to accurately determine the degree of hand-loading, and therefore the degree of compensation to apply to retune the antenna to the correct frequency, and to maximize power transfer into the antenna. However, this solution can be problematic if the antenna is a receive-only antenna, as in the case of a diversity LTE antenna which is receive only. If no power can be applied directly to the antenna, it is difficult to know the antenna performance.
The only way currently to assess the antenna performance is to measure the quality of the received data. This, however, is a measurement of the entire system, including the base station and the channel condition due to obstructions between the handheld unit and the signal source (the base station).
Accordingly, what is needed is a technique to measure antenna performance while a communication device is in use. It would also be of benefit to provide a technique that can measure a receive-only antenna, and to measure an antenna in close proximity to another antenna.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.